Cryptobioturbation and the Work of Sedimentologically Friendly Organisms

Pemberton, S. George¹, James A. MacEachern², Murray K. Gingras¹, Thomas Saunders³ (1) University of Alberta, Edmonton, AB (2) Simon Fraser University, Burnaby, BC (3) University of Alberta, Edmonton

Biogenic chaos, from an ichnological point of view, can be defined as total bioturbation of sediment by organisms, such that the original sedimentary fabric and associated sedimentary structures are destroyed. Nevertheless, not all forms of thorough bioturbation are purely destructive. As improbable as it first sounds, sediment can be pervasively (potentially 100%) bioturbated, and yet have suffered little distortion of original bedding. Owing to its diminutive and obscure nature, cryptobioturbation has not received widespread attention. As the name implies, cryptobioturbation is characteristically small in scale and exceedingly subtle in expression. What sets it apart from other forms of bioturbation, however, is the tendency to preserve, rather than to destroy, the sediment's primary physical structure. The fabric that results from crytobioturbation can have significant influence on resulting permeability and porosity trends. The effect of the cryptic bioturbation does not result in enhanced permeabilities, but rather, promotes a reduction in internal heterogeneities, leading to a more uniform permeability distribution. Similar cryptically bioturbated facies are very widespread in the rock record and have been encountered in the Berriasian Toro Sandstone in the Iagifu field, Papua New Guinea and the Eocene Mirador Formation in the Cusiana field, Colombia. The effects are expected to be most dramatic in gas-prone systems. Cryptobioturbation can, therefore, result in a thoroughly bioturbated sedimentary media, in which primary sedimentary structures are not destroyed but rather, remain visible. This phenomenon is also seen in some macro-burrows like Macaronichnus, where the burrowing process does not lead to wholesale destruction of the sedimentary fabric.